From c1bf7a2b9bc5e8128cce309b01a41cb3ee5afcc3 Mon Sep 17 00:00:00 2001
From: lexlian <9305752+lexlian@users.noreply.github.com>
Date: Fri, 22 May 2026 19:12:58 +0800
Subject: [PATCH] fix(session): inline @agent mention uses agent's configured
 model

Closes #28809

When mentioning an agent inline (e.g. "@other hello"), the agent name
lives in the parts array as AgentPartInput. createUserMessage was only
reading input.agent (top-level field set by UI agent switch), which
remains unset for inline mentions, causing a fallback to the default
agent's model instead of the mentioned agent's configured model.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
---
 packages/opencode/src/session/prompt.ts       |  2 +-
 packages/opencode/test/session/prompt.test.ts | 51 +++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index fc9fa0b96a8c..43a05e03f41c 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -686,7 +686,7 @@ export const layer = Layer.effect(
     })
 
     const createUserMessage = Effect.fn("SessionPrompt.createUserMessage")(function* (input: PromptInput) {
-      const agentName = input.agent
+      const agentName = input.agent ?? input.parts.find((p): p is MessageV2.AgentPartInput => p.type === "agent")?.name
       const ag = agentName ? yield* agents.get(agentName) : yield* agents.defaultInfo()
       if (!ag) {
         const available = (yield* agents.list()).filter((a) => !a.hidden).map((a) => a.name)
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index ff9ded4d1927..fc81bfc7a0df 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -2227,6 +2227,57 @@ noLLMServer.instance(
   },
 )
 
+// Inline agent mention uses agent's configured model
+
+it.instance(
+  "inline @agent mention uses the agent's configured model instead of default",
+  () =>
+    Effect.gen(function* () {
+      const prompt = yield* SessionPrompt.Service
+      const sessions = yield* Session.Service
+      const session = yield* sessions.create({})
+
+      const msg = yield* prompt.prompt({
+        sessionID: session.id,
+        noReply: true,
+        parts: [
+          { type: "agent", name: "other" },
+          { type: "text", text: "hello from other agent" },
+        ],
+      })
+
+      if (msg.info.role !== "user") throw new Error("expected user message")
+      expect(msg.info.model.providerID).toBe(ProviderID.make("test"))
+      expect(msg.info.model.modelID).toBe(ModelID.make("test-model-2"))
+
+      yield* sessions.remove(session.id)
+    }),
+  {
+    config: {
+      ...cfg,
+      provider: {
+        ...cfg.provider,
+        test: {
+          ...cfg.provider.test,
+          models: {
+            ...cfg.provider.test.models,
+            "test-model-2": {
+              ...cfg.provider.test.models["test-model"],
+              id: "test-model-2",
+              name: "Test Model 2",
+            },
+          },
+        },
+      },
+      agent: {
+        other: {
+          model: "test/test-model-2",
+        },
+      },
+    },
+  },
+)
+
 // Agent / command resolution errors
 
 noLLMServer.instance(